Microplastic pollution and ecological risk in estuaries and coastal areas: A case study at Han River estuary, Da Nang city, Vietnam

Microplastic pollution and ecological risk in estuaries and coastal areas: A case study at Han River estuary, Da Nang city, Vietnam | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Microplastic pollution and ecological risk in estuaries and coastal areas: A case study at Han River estuary, Da Nang city, Vietnam Nguyen Thi Thanh Hoai, Ta Le Dang Khoi, Le Trung Son, Nguyen Lai Thanh, and 10 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7419673/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Microplastics (MPs) pollution has been identified as a significant environmental concern in various ecosystems, including estuarine and coastal waters. In this study, surface and column water samples from the Han River (Vietnam) were collected during the rainy season of 2023 and the dry season of 2024 and analyzed. Microplastic characteristics were determined based on quantity, shape, size, color, polymer composition, and Pollution Load Index (PLI). Microplastics were detected at all sampling locations, with marked spatial and seasonal variability. Total MPs abundance in the dry season was consistently lower than in the rainy season. In the rainy season, MPs density in column water exceeded that in surface water, whereas the reverse pattern was observed in the dry season. Microfragments and microfibers of smaller size classes predominated. White was the most common color, followed by blue, green, red, and other colors. The number of polymer types in the rainy season was 22 and decreased to 5–6 in the dry season. Polyethylene terephthalate (PET) accounted for the highest proportion of all samples. The calculated PLI value (1.74) was classified as “Hazard Level I,” indicating a low pollution load; however, the potential environmental risks posed by microplastics remain a concern. Clinical trial number: not applicable Microplastics water column surface water pollution Pollution Load Index (PLI) Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 1. Introduction Plastic has become extremely popular in everyday life and possesses some advantage features in comparison to other materials due to its versatility, affordability, durability, and resistance to a wide range of temperatures (Andrady 2017 ; Wootton et al. 2022 ). Its inert nature and long lifespan make it widely applicable in various industries, including household goods, personal items, textiles, packaging, and construction (Geyer et al. 2017 ). Therefore, global plastic production has surged dramatically since its large-scale manufacturing began in the 1950s, reaching 413.8 million tons in 2023 (Plastics Europe 2023), causing increased potential risk to the ecosystem in general and human health in particular due to exposure. While a portion of plastic waste is managed through recycling or incineration (9%), vast quantities (90%) remain in the environment, contributing significantly to marine pollution (Geyer et al. 2017 ; OECD 2022). Over time, these plastics degrade into microplastics, which accumulate in water, sediments, and living organisms, posing severe threats to ecosystems, and human health. According to NOAA (2015) and FAO ( 2022 ), microplastics (MPs) are defined as tiny plastic pieces smaller than 5 mm in size and are emerging groups of pollutants that have received particular attention recently. They are diveded to two groups including primary and secondary MPs. Primary MPs are intentionally manufactured at small sizes for use in industrial products, personal care items, and abrasives, while secondary MPs are derived from the degradation of larger plastic debris due to environmental factors such as UV radiation, mechanical forces, and microbial activity (Lapyote et al. 2023). MPs are not only widely dispersed in freshwater and marine systems (Lin et al. 2022 ; Xiong et al. 2022 ; Matias et al. 2023 ) but also accumulate in sediments and a variety of organisms, potentially posing risks to ecosystems and human health through seafood consumption (Horton et al. 2021 ). Vietnam, like many other countries, is facing an escalating crisis of plastic pollution. As a rapidly developing nation with extensive coastlines and a high dependence on marine resources, Vietnam generates a substantial amount of plastic waste, much of which ends up in the environment. Among these, microplastics pose a unique challenge due to their persistence, ability to bioaccumulate, and potential toxic effects on aquatic organisms and human health. The water environment, particularly estuarine and coastal ecosystems, is highly susceptible to microplastic contamination. Estuaries, where freshwater meets seawater, serve as critical habitats for diverse marine species and act as natural filters for pollutants. However, they are also key accumulation zones for microplastics due to urban runoff, industrial discharge, and riverine inputs. The presence of microplastics in estuaries and coastal waters can lead to severe environmental consequences, including the disruption of aquatic food chains, habitat degradation, and threats to fisheries and public health. The Han River, located in Da Nang City, Vietnam, is a vital waterway that flows through the heart of the city before emptying into the East Sea. As a dynamic estuarine system, it is subject to various anthropogenic influences, including urbanization, tourism, and industrial activities. The river plays a crucial role in the socio-economic development of Da Nang, supporting fisheries, transportation, and recreational activities. However, like many other riverine systems in Vietnam, the Han River is increasingly threatened by plastic pollution, particularly microplastics. Despite its significance, limited research has been conducted to assess the extent of microplastic contamination in the Han River estuary and its potential environmental impacts. Given the growing concern over plastic pollution in Vietnam’s aquatic environments, this study aims to investigate the status of microplastic contamination in water environment the Han River estuary. The research will focus on identifying the discharging sources, and characteristics of microplastics in the surface water and column water in the estuary. The findings will provide valuable insights into the extent of microplastic pollution in the region and contribute to the development of effective management strategies to mitigate its impact. This research aims to: Assess the abundance and characteristics of microplastics in the Han River estuary. Identify the potential sources of microplastic pollution in the study area. Evaluate the ecological risks associated with microplastic contamination in the estuarine environment. Urgency of the Study The rapid increase in plastic pollution in Vietnam’s water environments, particularly in estuaries and coastal ar eas, calls for immediate attention. Microplastic contamination poses serious threats to biodiversity, water quality, and human health, necessitating urgent research and policy interventions. The Han River estuary, as a crucial water body in Da Nang City, requires systematic assessment to understand the severity of microplastic pollution and formulate appropriate mitigation strategies. This study is expected to fill critical knowledge gaps and contribute to sustainable water resource management in Vietnam. By addressing these key issues, the study will not only enhance scientific understanding of microplastic pollution in estuaries but also provide a foundation for future environmental conservation efforts in Da Nang and other coastal cities in Vietnam. 2. Methodology 2.1. Characteristics of area study Da Nang, situated in the South-Central region of Vietnam, holds a pivotal position as the most significant urban center in the Central region. It serves as a hub for various sectors, including economics, finance, politics, culture, tourism, society, education, science, and technology. Geographically, Da Nang is located between latitudes 15°55' and 16°14' North, and longitudes 107°18' and 108°20' East. The Han River is one of the four principal rivers in Da Nang City along with the Vu Gia, Cu De, and Phu Loc rivers, plays a crucial role in supporting the city’s socio-economic development. It is located downstream of the Thu Bon River and originates at the confluence of the Cam Le and Vinh Dien rivers. The Han River extends approximately 7.2 kilometers and flows through the urban area. There are many restaurants, hotels and people living on both sides of the river. This is also a famous and important tourist destination of the city. Waterway traffic and fishing activities in the estuary also generate a lot of organic waste into the environment, including plastic. The eight sampling sites, positioned along a transect from Tien Son Bridge toward Da Nang Bay (Fig. 1 and Table 1 ), were characterized by the presence of various sources of waste or human activities associated with waste discharge. Table 1 Sampling location characteristics No. Sampling Location Sample Code Description 1 Tien Son Bridge ĐN1 Located near residential areas of My An, Hoa Cuong Bac, and Hoa Cuong Nam wards in Ngu Hanh Son District. 2 Tran Thi Ly Bridge ĐN2 Surrounded by residential areas and restaurants, near Green Island villa area and Dinh Tien Hoang Primary School in Binh Thuan Ward. 3 Rong Bridge ĐN3 Adjacent to residential areas and numerous restaurants in An Hai Tay and Hai Chau 1 Wards. 4 Han River Bridge ĐN4 Flanked by hotels, restaurants, and supermarkets in An Hai and Son Tra Wards, within Hai Chau and Son Tra Districts. 5 City Discharge Drain ĐN5 This location marks the discharge point from Da Nang City into the Han River, near Da Phuoc (Old) fishing port and Da Nang Marina in Thuan Phuoc and Hai An Bac Wards. 6 Thuan Phuoc Bridge ĐN6 Situated near the Thuan Phuoc lighthouse, surrounded by hotels and restaurants, with no residential areas, in Thuan Phuoc and Nai Hien Dong Wards. 7 Da Nang Bay 7 ĐN7 Located at the confluence of the Han River and Da Nang Bay, approximately 700 meters from Thuan Phuoc Bridge (ĐN6). 8 Da Nang Bay 8 ĐN8 Situated 800 meters from ĐN7 within Da Nang Bay, with no surrounding residential areas. 2.2. Sampling Method The sampling method was conducted following established protocols outlined in previous studies (Masura et al. 2015 ; Sliva et al. 2017). A neuston mesh net with a mesh size of 330 µm was either mounted on a water collection box or integrated with a Manta trawl net (dimensions: 30 x 30 x 15 cm, D x W x H). A flowmeter was affixed to the system to measure the volume of water filtered during sampling. At every location, the equipment was secured to boats, and the collection boxes were allowed to float on the water surface ranging from 30 to 60 minute to capture all solid particles present in both the surface layer and water column, including plastic debris and other suspended solids. The samples were conducted spanning from rainy season (October 2023) to dry season (May 2024). All collected samples were stored in dark glass containers at 4°C and transported to the laboratory on the same day for further analysis. 2.3. Analysis Methods The identification and characterization of microplastics were conducted using the wet peroxide oxidation method. Firstly, 300 mL of original wastewater was wet sieved by a stainless-steel mesh screen 5 mm. The sieved samples containing particles smaller than 5 mm remained for next experiments. Subsequently, the samples were pretreated to remove organic matter by adding solution 30% hydrogen peroxide (H₂O₂) and the Fe(II) 0.05 M (Merck, Germany) at 40°C for 48 hours, following modified NOAA procedures (Masura et al., 2015 ). Density separation was then conducted to isolate microplastics. A saturated NaI solution (density ≈ 1.6 g/cm³) was added to the digested samples. The mixture was allowed to settle, and the supernatant was collected and filtered through a 1.6 µm pore size glass fiber filter (Whatman, Germany) by vacuum pump and glass filtration apparatus (Duran, Germany). The microplastic characteristics such as quantity, size, shape and color were observed under optical stereomicroscope (MSZ5000-T-IL-TL, Kruss, Germany) (Masura et al. 2015 ). For Fluorescence Microscope method, the microplastics was stained by Nile Red (9-diethylamino-5H-benzo[α]phenoxazine-5-one), a lipophilic dye that preferentially binds to hydrophobic plastic surfaces. The staining procedure followed methods adapted from Erni-Cassola et al. ( 2017 ). Each sample filter was stained with 1 mL of Nile Red working solution (1µg/mL in ethanol) and incubated in the dark at room temperature for 30 minutes. After staining, filters were gently rinsed with deionized water and dried in a petri dish under a hood cabinet. Filters were examined under a fluorescence microscope and only particles fluorescing after Nile Red staining and confirmed via morphology were counted as microplastics. The microplastic characteristics such as quantity, size, and shape were observed with Fluorescence Microscope (AXIO Zoom V16, Zeiss, Germany). Then, the quantity, size and polymer types present in the samples were also classified with a FTIR-6800 system (Nicolet iN10MX, USA). The spectra obtained from every sample were compared with the corresponding standard spectra in the spectral library (Jung et al. 2018 ). Quality Assurance and Control: Strict anti-contamination protocols were implemented throughout sample processing. Procedural blanks were analyzed to ensure no interferences from lab materials. All substrates and tools used in analysis were cleaned with ethanol and deionized water and inspected before use. 2.4 Pollution Load Index To evaluate the MP pollution levels in the surface and column water of Han River, the integrated Pollutant Load Index (PLI) was applied in accordance with the method reported by Tomlinson et al. ( 1980 ). The PLI index enables the classification of contamination risk such as below 10 categorized as (I) low risk, from 10 to 20 as (II) moderate risk, from 20 to 30 as (III) high risk, and above 30 as (IV) very high risk (Table S1). The PLI index was calculated using the following equation: PLI Si = \(\:\sqrt{\frac{{C}_{si}}{{C}_{0}}}\) PLI local = \(\:\sqrt[n]{{{PLI}_{S1.}\:{PLI}_{S2}\dots\:.PLI}_{Sn}}\) In this formula, “Csi” refers to the MP concentration measured at each sampling location, whereas “C 0 ” denotes the lowest MP abundance recorded in the present study, representing the uncontaminated condition due to the absence of an absolute zero reference value. Table S1 Classification table of Pollution load index for MP pollution (Tomlinson et al., 1980 ; Ranjani et al., 2021 ) PLI Risk category 30 Very high risk 2.5. Statistical data The database in the present study is calculated by GraphPad 6 and Original 2019b software. The volume of water was recorded from the flowmeter for subsequent calculations. The density of microplastics was determined using the following formula (Do et al. 2022): where C denotes the microplastic density (fragment, fiber, particle/m³), n represents the number of microplastic items in the sample (fragment, fiber, particle), and V corresponds to the volume of water filtered through the mesh (m³). 3. RESULT AND DISCUSSION 3.1. The microplastic density classification by quantity Different analytical methods showed different results and the results in Table 2 showed that the microplastic density in both two seasons are also very different. In the rainy season, the presence of microplastics was observed at all 8 sampling locations. The microplastic density was determined by stereomicroscope, Fluorescence Microscope and FTIR method varied from 1201, 1049, 1260 MPs.L -1 in surface water samples to 1408, 1254, 1500 MPs.L -1 in column water samples, respectively. The results also showed that ĐN6 consistently exhibited the highest microplastic density regardless of the analytical method applied. This finding is consistent with field observations, as the site is located near the municipal wastewater discharge area. The density of microplastics in the dry season is significantly different from the rainy season. These values decrease substantially and, in some locations (ĐN7 and ĐN1), microplastics even were not recorded at all. The corresponding density values were 148, 177 and 116 MPs.L -1 in surface water samples and 123, 162 and 48 MPs.L -1 in column water samples. Table 2 Total of microplastics in surface water (ĐN_SW) and water column (ĐN_CW) samples at Han River estuary were analyzed by three methods: stereomicroscope, Fluorescence Microscope and FTIR Code sample Quantity of microplastic in rainy season Stereomicroscope method Fluorescence Microscope method FTIR method ĐN_SW ĐN_CW ĐN_SW ĐN_CW ĐN_SW ĐN_CW ĐN1 50 171 45 150 50 180 ĐN2 220 194 195 168 225 205 ĐN3 49 142 35 110 50 150 ĐN4 49 187 41 178 55 200 ĐN5 108 137 95 115 120 145 ĐN6 489 334 416 320 500 360 ĐN7 92 148 90 128 105 155 ĐN8 144 95 132 85 155 105 Total 1201 1408 1049 1254 1260 1500 Code sample Quantity of microplastic in dry season Stereomicroscope method Fluorescence Microscope method FTIR method ĐN_SW ĐN_CW ĐN_SW ĐN_CW ĐN_SW ĐN_CW ĐN1 19 13 28 13 28 0 ĐN2 10 20 14 10 8 4 ĐN3 13 6 13 37 8 8 ĐN4 25 17 46 28 28 16 ĐN5 6 14 23 11 28 8 ĐN6 45 25 22 28 4 0 ĐN7 20 8 24 10 0 8 ĐN8 10 20 7 25 12 4 Total 148 123 177 162 116 48 The findings of this study align with some previous research in estuaries area (Hidalgo-Ruz et al. 2012 ; Liu et al. 2021 ; Gao et al. 2023 ) but contrast with others (Lebreton et al. 2017 ; Dai et al. 2018 ; Tikhonova et al. 2024 ). MPs abundance was consistently lower in the dry season than in the rainy season; in the rainy season, water column densities exceeded surface water, while the opposite was observed in the dry season. As noted by Hidalgo-Ruz et al. ( 2012 ) and Gao et al. ( 2023 ), low-density MPs can remain longer in surface layers, increasing organisms’ exposure. The major source of MPs into the marine environment is through riverine systems, influenced by water depth, wind direction, flow velocity and human activities (Lebreton et al. 2017 ; Dai et al. 2018 ; Lenaker et al. 2019 ; Tikhonova et al. 2024 ). Table 2 showed that the number of microplastics detected varied markedly among the sampling locations, exhibiting a decreasing trend toward the river mouth. The last two locations recorded relatively low numbers of microplastics, a result consistent with their geographical characteristics, location, and surrounding landscape, as both riverbanks are uninhabited, and few services and production activities. Similar spatial patterns have been documented globally: Li et al. ( 2020 ) found higher MPs density in estuaries than offshore islands, while Diana et al. ( 2022 ) reported much higher concentrations in the Sado estuary (1042.8 ± 430.8 MPs/kg) compared to coastal locations (52.9 ± 31.9 MPs/kg), with densities increasing inland due to human activities. Further inland, microplastic density was found to increase, closely related to the daily activities of residents along both riverbanks. Morever, MPs density is also affected by weather conditions and tidal regimes as well as regional rainfall and flooding. The coastal waters of Da Nang are influenced by a semi-diurnal tidal regime with an amplitude of about 0.6 m. The Han River, flowing uniquely from south to north into Da Nang Bay, is characterized by short length, steep slope, large flow fluctuations, and low sediment loads. During the rainy season, rapid floods occur but last only a few days, while in the dry season, reduced upstream supply lowers water levels and causes salinization. There are many residential areas, numerous restaurants, hotels, supermarkets, local markets located along its banks and a fishing port near the river mouth. A large amount of waste from terrestrial sources is received by the river during flood events, explaining the higher microplastic density in the rainy season. According to Lebreton et al. ( 2017 ), more than 74% of the annual plastic waste discharged from rivers occurs between May and October, as reported in the summary on microplastic pollution in Asia and East Asia. These results are consistent with regional studies and highlight surface runoff as the main mechanism transporting microplastics from land to river and into the marine environment (Andrady 2017 ). 3.2. The microplastic density classification in size Size-based classification of microplastics showed seasonal differences across analytical methods. Using stereomicroscope and fluorescence microscope, smaller particles were dominant in the rainy season (20–50, 50–150, 100–300, 300–500, > 500 µm), while larger ones prevailed in the dry season (200–500, 500–1000, 1000–1500, > 1500 µm). Although particles were sieved out, some long fibers (> 1.5 mm) were detected because their curled form allowed them to pass through the mesh before expanding during oxidation. In contrast, FTIR consistently identified five size categories: 20–50, 50–150, 100–300, 300–500, and > 500 µm. a) Stereomicroscope method For the classification using stereomicroscope, the rainy season survey showed that microplastics sized 300–500 µm were most abundant in both surface water (631 MPs·L⁻¹) and water column (704 MPs·L⁻¹), while particles > 500 µm were least common (37 and 60 MPs·L⁻¹, respectively). In surface water, the maximum count for 300–500 µm particles was at location ĐN6 (265 MPs·L⁻¹) and the minimum for > 500 µm at ĐN4 location (2 MPs·L⁻¹); in the water column, the highest was also at ĐN6 location (116 MPs·L⁻¹) and the lowest at ĐN5 location (5 MPs·L⁻¹). During the dry season, microplastics of 200–500 µm dominated, with 112 MPs·L⁻¹ in surface water and 104 MPs·L⁻¹ in the water column, followed by 500–1000 µm (32 and 12 MPs·L⁻¹) and 1000–1500 µm (3 and 6 MPs·L⁻¹). Microplastics > 1500 µm were rare, detected only at ĐN1 location (surface water) and ĐN2 location (water column), and absent at other locations (Table 3 ). Table 3 The microplastics size in surface water (ĐN_SW) and water column (ĐN_CW) samples at Han River estuary by stereomicroscope method Code sample Size of microplastic in the rainy season 20–50 µm 50–150 µm 150–300 µm 300–500 µm > 500 µm ĐN_SW ĐN_CW ĐN_SW ĐN_CW ĐN_SW ĐN_CW ĐN_SW ĐN_CW ĐN_SW ĐN_CW ĐN1 15 21 7 33 5 10 20 99 3 8 ĐN2 45 38 20 33 5 12 145 104 5 7 ĐN3 18 28 9 19 6 9 12 81 4 5 ĐN4 10 30 17 39 7 11 13 98 2 9 ĐN5 18 24 11 17 6 11 68 79 5 6 ĐN6 105 116 82 57 27 39 265 110 10 12 ĐN7 34 27 16 17 10 10 27 88 5 6 ĐN8 29 22 10 15 21 6 81 45 3 7 Total 274 306 172 230 87 108 631 704 37 60 Code sample Size of microplastic in the dry season 200–500 µm 500–1000 µm 1000–1500 µm > 1500 µm ĐN_SW ĐN_CW ĐN_SW ĐN_CW ĐN_SW ĐN_CW ĐN_SW ĐN_CW ĐN1 14 12 3 1 1 0 1 0 ĐN2 8 17 2 2 0 0 0 1 ĐN3 11 3 2 2 0 1 0 0 ĐN4 17 15 8 2 0 0 0 0 ĐN5 2 11 4 2 0 1 0 0 ĐN6 40 21 3 1 2 3 0 0 ĐN7 12 7 8 1 0 0 0 0 ĐN8 8 18 2 1 0 1 0 0 Total 112 104 32 12 3 6 1 1 b) Fluorescence Microscope Method Similarly, fluorescence microscopy identified five size groups in the rainy season and four in the dry season. In the rainy season, microplastics were detected at all sites across all groups, with the highest concentration in the 300–500 µm range (570 MPs·L⁻¹ in surface water and 662 MPs·L⁻¹ in the water column) and the lowest in the > 500 µm group (22 and 36 MPs·L⁻¹, respectively). In the dry season, the 200–500 µm group dominated, reaching 148 MPs·L⁻¹ in surface water and 140 MPs·L⁻¹ in the water column. Microplastics > 1500 µm were extremely rare, with only one particle (1 MPs·L⁻¹) detected in surface water and none in the water column (Table 4 ). Table 4 The microplastics size in surface water (ĐN_SW) and water column (ĐN_CW) samples at Han River estuary by Fluorescence Microscope method Code sample Size of microplastic in the rainy season 20–50 µm 50–150 µm 150–300 µm 300–500 µm > 500 µm ĐN_SW ĐN_CW ĐN_SW ĐN_CW ĐN_SW ĐN_CW ĐN_SW ĐN_CW ĐN_SW ĐN_CW ĐN1 10 18 12 30 7 8 11 89 5 5 ĐN2 36 32 27 28 3 10 126 95 3 3 ĐN3 10 20 12 12 4 5 7 73 2 1 ĐN4 9 28 15 35 5 9 11 99 1 7 ĐN5 14 18 9 12 4 8 65 72 3 4 ĐN6 78 105 66 57 18 36 250 114 4 8 ĐN7 30 25 24 15 8 8 25 77 3 3 ĐN8 25 20 15 12 16 5 75 43 1 5 Total 212 266 180 201 65 89 570 662 22 36 Code sample Size of microplastic in the dry season 200–500 µm 500–1000 µm 1000–1500 µm > 1500 µm ĐN_SW ĐN_CW ĐN_SW ĐN_CW ĐN_SW ĐN_CW ĐN_SW ĐN_CW ĐN1 21 12 4 1 2 0 1 0 ĐN2 11 8 3 1 0 1 0 0 ĐN3 10 27 3 9 0 1 0 0 ĐN4 41 27 5 1 0 0 0 0 ĐN5 19 10 3 1 1 0 0 0 ĐN6 19 27 2 1 1 0 0 0 ĐN7 21 8 3 2 0 0 0 0 ĐN8 6 22 1 3 0 0 0 0 Total 148 140 24 20 4 2 1 0 c) FTIR method In contrast, FTIR classification identified only five size groups in both seasons. During the rainy season, the 50–150 µm group showed the highest density (655 MPs·L⁻¹ in surface water and 675 MPs·L⁻¹ in the water column), while the 300–500 µm group had the lowest values (80 and 90 MPs·L⁻¹, respectively). Microplastics from all five groups were found at most locations, except ĐN8 location (Table 5 ). In the dry season, overall densities declined, but the 50–150 µm group remained dominant (48 MPs·L⁻¹ in surface water and 16 MPs·L⁻¹ in the water column). Other groups appeared sporadically, with many locations showing no detection. The > 500 µm group recorded the lowest values (12 and 4 MPs·L⁻¹, respectively), detected only at ĐN3, ĐN4, and ĐN6 locations (Table 5 ). Table 5 The microplastics size in surface water (ĐN_SW) and water column (ĐN_CW) samples at Han River estuary by FTIR method Code sample Size of microplastic in the rainy season 20–50 µm 50–150 µm 150–300 µm 300–500 µm > 500 µm ĐN_SW ĐN_CW ĐN_SW ĐN_CW ĐN_SW ĐN_CW ĐN_SW ĐN_CW ĐN_SW ĐN_CW ĐN1 10 30 25 80 5 20 5 30 5 20 ĐN2 35 70 110 90 45 20 15 10 20 15 ĐN3 20 40 10 55 5 20 10 15 5 20 ĐN4 15 80 25 70 10 15 0 10 5 25 ĐN5 45 35 35 55 20 25 15 10 5 20 ĐN6 60 115 310 190 55 40 25 5 50 10 ĐN7 20 15 50 95 15 30 5 10 15 5 ĐN8 35 45 90 40 0 10 5 0 25 10 Total 240 430 655 675 155 180 80 90 130 125 Code sample Size of microplastic in the dry season 20–50 µm 50–150 µm 150–300 µm 300–500 µm > 500 µm ĐN_SW ĐN_CW ĐN_SW ĐN_CW ĐN_SW ĐN_CW ĐN_SW ĐN_CW ĐN_SW ĐN_CW ĐN1 0 0 24 0 0 0 4 0 0 0 ĐN2 4 0 4 4 0 0 0 0 0 0 ĐN3 0 0 4 4 0 4 0 0 4 0 ĐN4 8 0 12 0 0 0 4 12 4 4 ĐN5 8 0 4 0 12 8 4 0 0 0 ĐN6 0 0 0 0 0 0 0 0 4 0 ĐN7 0 4 0 4 0 0 0 0 0 0 ĐN8 8 0 0 4 4 0 0 0 0 0 Total 28 4 48 16 16 12 12 12 12 4 The results also highlighted heterogeneity in microplastic sizes across surface and column water samples. Variations between analysis methods may explain the observed discrepancies, as the two types of microscopes yielded different distributions by size group, though the exact reason remains unclear. Nonetheless, most microplastics were concentrated in the < 500 µm size range (Tables 3 , 4 , and 5 ), and in some locations no microplastics of other size classes were detected. This suggests that microplastic pollution has persisted in the area surveyed over an extended period. Over time, smaller-sized microplastics become more easily transported by wind and water, leading to gradual accumulation in the environment. Similar patterns have been reported in previous studies (Mato et al. 2001 ; Teuten et al. 2009 ; Hernandez et al. 2017 ; Alam et al. 2019). Plastic debris has also been shown to interact with biological processes and facilitate pollutant accumulation due to its strong adsorption capacity (Mato et al., 2001 ; Teuten et al., 2009 ). Larger microplastics can degrade into smaller particles under the influence of sunlight, wind, and hydrodynamic forces when persisting in the environment for a long time. Lenaker et al. ( 2019 ) further demonstrated that polymer density decreases with depth in the water column and that microplastics tend to accumulate in sediments as they are transported from discharge points to estuarine areas. 3.3. The microplastic density classification in shape Four microplastic types were detected in both surface and water column samples at the Han River estuary including fibers, fragments, particles, and others. All three methods showed that fragments dominated in the rainy season and fibers in the dry season (Fig. 2 ). a) Stereomicroscope method Stereomicroscopy analysis showed that in the rainy season, fragments were dominant in both surface and water column samples, accounting for up to 60.13%, followed by fibers (36% and 33.33%). Particles and other types were less abundant, ranging from 0.58% in surface water to 5.87% in column water (Fig. 3 ). In contrast, during the dry season, fibers were dominant (47% in surface water and 65.4% in column water), while fragments were secondary (26.8% and 18.5%). The remaining forms varied between 2.4% (column water) and 22.5% (surface water) (Fig. 3 ). b) Fluorescence Microscope Method Fluorescence microscopy showed a clear seasonal shift in microplastic forms. During the rainy season, fragments dominated, accounting for 62.92% of water column samples and 69.25% of surface water, followed by fibers (31.64% and 27.37%). Other forms were rare, ranging from 0.20% in surface water to 4.96% in the water column (Fig. 4 ). In the dry season, fibers became predominant (69.93% in the water column and 54.15% in surface water), while fragments ranked second (23.44% and 39.42%). The proportions of other forms remained low, between 2.15–4.28% in surface water and 3.18–3.46% in the water column (Fig. 4 ). c) FTIR method FTIR analysis identified only fragments and fibers in both surface and column water samples, in contrast to stereomicroscope and fluorescence methods, which detected additional forms (Fig. 5 ). In the rainy season, fragments were dominant, accounting for 65.08% in surface water and 62.10% in the water column, followed by fibers (32.14% and 30.67%); particles were detected at low proportions (2.78% and 7.27%). No other shapes were observed. In the dry season, only fragments and fibers were recorded, with fibers prevailing in both surface and column water (58.62% and 58.33%), while fragments accounted for 41.38% and 41.67%, respectively (Fig. 5 ). The distribution of microplastic forms in both surface and column water samples showed clear seasonal and vertical variations, influenced by hydrological conditions and water dynamics, making MPs form an important pollution indicator (Pushan et al. 2022 ). In this study, fragments dominated during the rainy season, while fibers were predominant in the dry season. The rainy-season dominance of fragments likely resulted from surface runoff and hydrodynamic forces (e.g., heavy rainfall, turbulent flow) breaking down larger plastics, consistent with findings in Da Nang (Nguyen et al. 2020 ; Do et al. 2022) and other regions in Vietnam (Nguyen et al., 2020 ; Nguyen et al., 2021 ; Strady et al., 2021 ). Fragments, often derived from packaging, cleaning products, cosmetics, and containers (Wu et al. 2019 ), were abundant due to floods transporting large debris downstream for mechanical degradation. In contrast, low flow in the dry season allowed fibers - mainly from discarded fishing gear (Montarsolo et al. 2018 ) - to dominate, as reduced physical disruption favored their persistence. Other forms such as foam and particles occurred at lower levels but remain concerned about their potential toxicity to aquatic organisms (Tanaka and Takada 2016 ). 3.4. The microplastic density classification in colors For color classification, only the stereomicroscope method was applied, as other techniques could be affected by equipment or staining interference. Results showed clear seasonal variations. In rainy season, white microplastics were dominant, accounting for 45% in surface water and 52.3% in column water, followed by blue (25.4% and 20.2%), green (15.9% and 15.9%), red (9.4% and 7.1%), and others (4.3% and 4.5%). In contrast, during the dry season, green microplastics were most abundant (49.5% in surface water and 46.7% in column water). White ranked second in surface water (22.9%), whereas black ranked second in column water (20.6%). The remaining colors showed lower proportions, with 13.9%, 5.8%, and 7.9% in surface water and 15.7%, 5.5%, and 11.5% in column water for white/black, red, and other colors, respectively (Fig. 6 ). The color of microplastics has been considered of particular concern because they can be mistaken for food by aquatic organisms (Cole et al. 2014 ; Sá et al. 2016 ; Li et al. 2021 ). Furthermore, color also indicates initial information regarding plastic production (Klein et al. 2015 ). In fact, colorless or transparent microplastics may be overlooked during extraction or identification. The results of this study are consistent with many previous publications showing that white is the dominant color among the recorded colors. Corcoran et al. ( 2015 ) noted that white microplastics were significantly more abundant than other colors, followed by pink and purple plastics. Li et al. ( 2020 ) also showed that white accounted for 64.7% of the total microplastics detected in sediments at the Yangtze River estuary (China), followed by blue, transparent, yellow, black, red, brown, and green. In this study, there was a difference in the dominant color between the two seasons. White and blue were dominant in the rainy season and white and green were dominant in the dry season. This may be because blue MP often originates from blue nylon lines of nets used in fishing activities, while white may originate from fishing gear (e.g., fishing lines and nets) (Jabeen et al. 2017) and may also fade due to weather (Hidalgo-Ruz et al. 2012 ). According to our field survey, most restaurants, hotels, residents, and traditional markets along both sides of the Han River primarily use white, green, or blue plastic bags, while fishing nets are typically white and green. 3.5. The microplastic density classification by polymer forms Polymer types of microplastics in water samples were identified using FTIR method (Fourier-transform infrared spectroscopy). In rainy season, 22 polymer types with a total of 1.260 and 1500 MPs·L⁻¹ were recorded in surface and column water samples such as PET (Polyethylene terephthalate), Nylon, Olefin, Polyester, Evoh Eval Film, Cellophane, Teflon, HDPE (High Density Polyethylene), LDPE (Low Density Polyethylene), PVC (Polyvinyl chloride)…. PET and nylon polymers were the most dominant polymer types in surface and column water samples with values of 61.47; 11.47% and 62.29; 11.65%, respectively (Fig. 7 ). Other polymer types were observed inconsistently across locatons with the lower proportions. In contrast, results from the dry season showed a substantial reduction in both the number and concentration of identified polymer types. Only five and sixpolymer types were found in surface and column water samples with values of 116 and 48 MPs·L⁻¹, respectively. No polymers were detected at ĐN7 location. PET and Nylon also were predominant in surface and column water samples with values of 51.72; 34.48% and 16.67; 25%, respectively (Fig. 7 ). The FTIR spectral analysis provided further confirmation of previously reported patterns of MPs pollution in estuarine and coastal waters. Consistent with the results obtained for MPs density, morphology, size, and color, the diversity of polymer types exhibited clear seasonal variation. In rainy season, 22 polymer types were identified, whereas only 6 polymer types were recorded in dry season. PET and PP are widely recognized as the most prevalent polymers in aquatic environments (Klein et al. 2015 ; Li et al. 2020 ; Diana et al. 2022 ). For example, Li et al. ( 2020 ) reported PET and PP proportions of 37.3 and 28.6% in Yangtze River estuary (China), while Diana et al. ( 2022 ) found PET to account for 41% in the Sado River estuary (Portugal). Similarly, Klein et al. ( 2015 ) detected up to 75% PET, PP, and polystyrene (PS) in the Rhine and Main rivers (Germany). In the present study, PET consistently dominated across seasons and sample types with 61.47% and 62.29% of MPs in surface and column water samples in rainy season, and this proportion in the dry season was 51.72% and 16.67%, respectively. Interestingly, nylon was the second most abundant polymer, comprising 11.47–11.65% in rainy season and rising sharply to 25-34.48% in dry season. This finding reflects the widespread use of nylon bags in commercial and domestic activities along both sides of the Han River. Minor polymers such as olefins, Teflon, and phenol resins were also detected, indicating diverse plastic inputs. For instance, olefins were likely introduced from fuel leakage associated with tourist boats, fishing ports, and naval vessels near the river mouth. Overall, the dominant polymers detected (PET, PE, PP, PS) correspond to widely produced plastics characterized by low cost, high consumption volume, and broad applications in both industry and daily life. Polyethylene (PE) is commonly used for bags, bottles, and packaging (Wu et al. 2019 ; Wang et al. 2021 ), PET originates largely from textiles (Gedik and Eryaşar 2020 ), PP is applied in agricultural films and packaging, and PS is employed in food containers, jewelry, and fishing gear (Klein et al. 2015 ; Zhou et al. 2016). 3.6. Risk Assessment Currently, the ecological risk index has been used to assess the risk of microplastics (MPs) in various ecosystems such as coastal sediments, estuaries, soils, mangrove forests, and the atmosphere (Tomlinson et el. 1980; Barletta et al. 2016; Deng et al. 2021 ; Pegado et al. 2021 ; Nishitha et al. 2022 ). Therefore, the Pollution Load Index (PLI) value was applied in this study to evaluate the ecological risk at the Han River estuary area, Da Nang, Vietnam (Fig. 8 ). The results indicated that all surveyed locations have low levels of MP pollution, with PLI values ranging from 0.89 (ĐN6 in surface water and ĐN2, ĐN8 in column water in dry season) to 9.59 (ĐN6 surface water in rainy season) (Fig. 8 a). The PLI local analysis revealed that the study area exhibited a low pollution load, with an average PLI value of 1.74 (Fig. 8 b), categorized as "Hazard Level I" (< 10 on the risk classification scale - Table S1). Although microplastic pollution was classified as low, it can still pose serious threats to ecosystem health, causing nutrient loss, gastrointestinal blockage in organisms, and the release of toxic substances. Moreover, MPs may act as vectors for other contaminants such as persistent organic pollutants and heavy metals, amplifying ecological risks and potentially impacting human health through the food chain. The Han River in Da Nang, Vietnam, is a key waterway supporting fisheries, transport, and recreation, but urban activities such as restaurants, markets, hotels, fishing, and ship repair yards are microplastic discharge potential sources. Monitoring these sectors is essential to reduce emissions and prevent higher PLI values that may harm ecosystems and communities in the future. Results show clear seasonal patterns: fragments dominate during high-flow conditions, while fibers prevail under low-flow conditions, especially in surface water. Vertical variation highlights differences in transport and sinking behavior, underscoring the need for stratified and seasonal monitoring of microplastics in aquatic systems. 4. Conclusion This study analyzed microplastic characteristics in surface and column water from the Han River estuary (Vietnam) across rainy and dry seasons, focusing on abundance, morphology, color, polymer composition, and risk assessment. Microplastics were found at all locations, with higher densities in the rainy season, and in column water during the rainy but not the dry season. Microfragments and microfibers of smaller size dominated, with white as the most common color, followed by blue, green, and red. Spatial variation reflected human activities along both riverbanks. These findings provide baseline data for the South-Central Coast estuaries and support further studies on toxicity, transport, and ecological impacts. Although the Pollution Load Index indicated “Hazard Level I,” suggesting low risk, potential ecological impacts remain a concern. Thus, detailed classification of plastic types and stronger policies to regulate plastic use are needed to mitigate microplastic pollution. Declarations Conflicts of interest The authors confirm that there are no conflicts of interest associated with this publication. Funding statement This article was developed as part of project KC562, code ĐTĐL.CN ÷ 53/22, titled 'Research and assessment of the accumulation and impact of microplastics on the estuarine ecosystem along the South-Central Coast'. The authors gratefully acknowledge the Vietnam Ministry of Science and Technology for funding the project and supporting the completion of this article. Author Contribution Writing-original draft and Writing-review & editing: Tran Thi Thu Huong; Database analysis and software: Tran Thi Thu Huong, Vu Thu Van, Hoang Van Luong; Investigation, collection samples and Analysis methodology: Nguyen Thi Thanh Hoai, Ta Le Dang Khoi, Le Trung Son, Nguyen Lai Thanh, Nguyen Van Hanh, Tran Anh Quan, Pham Xuan Nui, Vu Kim Thu, Bui Thi Thu, Le Hung Phu, Vu Thu Van, Nguyen Bich Ngoc, Hoang Van Luong, Tran Thi Thu Huong. All authors have read and agreed to the published version of the manuscript. Acknowledgement This article was developed as part of project KC562, code ĐTĐL.CN÷53/22, titled 'Research and assessment of the accumulation and impact of microplastics on the estuarine ecosystem along the South-Central Coast'. The authors gratefully acknowledge the Vietnam Ministry of Science and Technology for funding the project and supporting the completion of this article. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7419673","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":523895917,"identity":"c17cf718-1071-44b1-b981-78e5beeeb2b5","order_by":0,"name":"Nguyen Thi Thanh Hoai","email":"","orcid":"","institution":"Vietnam Institute of Meteorology, Hydrology and Climate Change","correspondingAuthor":false,"prefix":"","firstName":"Nguyen","middleName":"Thi Thanh","lastName":"Hoai","suffix":""},{"id":523895918,"identity":"1202e098-5184-42dc-8c9a-73185384dad2","order_by":1,"name":"Ta Le Dang Khoi","email":"","orcid":"","institution":"Nha Trang 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06:46:16","extension":"xml","order_by":19,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":223089,"visible":true,"origin":"","legend":"","description":"","filename":"7c6bace6c3ee4287b12f4707535744c61structuring.xml","url":"https://assets-eu.researchsquare.com/files/rs-7419673/v1/4090de50cf91ba46f9b0d5eb.xml"},{"id":93006196,"identity":"d3447825-9da3-4ca6-893a-2ed55d35945e","added_by":"auto","created_at":"2025-10-08 06:46:16","extension":"html","order_by":20,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":236062,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-7419673/v1/0db373f141bd2ab06c9e1bab.html"},{"id":93006176,"identity":"80d3e03b-a49e-4733-bb0e-cdd7513e1bb2","added_by":"auto","created_at":"2025-10-08 06:46:15","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":133268,"visible":true,"origin":"","legend":"\u003cp\u003eSampling location area\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7419673/v1/7fe6207e2617dd622074de6a.jpg"},{"id":93007633,"identity":"7651fded-9e49-4711-8014-fd6ceb0b1b98","added_by":"auto","created_at":"2025-10-08 06:54:15","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":111903,"visible":true,"origin":"","legend":"\u003cp\u003eA variety of microplastic recovered from surface and column water samples in Han River estuary (Da Nang) were visualized. Microplastics were identified as follows: A-H were identified by stereomicrosope method; I-W were identified by Fluorescense microsope method.\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7419673/v1/0ac6e43f000828b8c5906c99.jpg"},{"id":93006180,"identity":"44833c64-5ac2-4277-9d62-32b99552a26a","added_by":"auto","created_at":"2025-10-08 06:46:15","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":69225,"visible":true,"origin":"","legend":"\u003cp\u003eAverage proportion of microplastic forms in water samples in Han River estuary by stereomicroscope method: (a) (b) Surface and column water samples in rainy season; (c) (d) Surface and column water samples in dry season.\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7419673/v1/9d5b6c75e0010a1ac37c0efd.jpg"},{"id":93007634,"identity":"018a3b78-dc13-4787-9e11-d44436039dfc","added_by":"auto","created_at":"2025-10-08 06:54:15","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":84087,"visible":true,"origin":"","legend":"\u003cp\u003eAverage proportion of microplastic forms in water samples in Han River estuary by Fluorescence Microscope method: (a) (b) Surface and column water samples in rainy season; (c) (d) Surface and column water samples in dry season.\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7419673/v1/15d338fccb74b841e932c07a.jpg"},{"id":93006179,"identity":"58111209-1325-462f-aef0-af888ec9c776","added_by":"auto","created_at":"2025-10-08 06:46:15","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":71056,"visible":true,"origin":"","legend":"\u003cp\u003eAverage proportion of microplastic forms in water samples in Han River estuary by FTIR method: (a) (b) Surface and column water samples in rainy season; (c) (d) Surface and column water samples in dry season.\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7419673/v1/f5ee8cb13cc6b6a62448c1aa.jpg"},{"id":93007635,"identity":"7c5f0c63-0616-4826-accd-97280496828f","added_by":"auto","created_at":"2025-10-08 06:54:16","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":134126,"visible":true,"origin":"","legend":"\u003cp\u003eMicroplastic colors in water samples in Han River estuary by stereomicroplastic method: (a) (b) Surface and column water samples in rainy season; (c) (d) Surface and column water samples in dry season.\u003c/p\u003e","description":"","filename":"6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7419673/v1/fd6fc48a7dbc2ccb389151f0.jpg"},{"id":93006199,"identity":"8a7c1cf1-b83d-4bc7-ad23-fd685236e440","added_by":"auto","created_at":"2025-10-08 06:46:16","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":176284,"visible":true,"origin":"","legend":"\u003cp\u003eThe polymer ratio in water samples in Han River estuary (Da Nang) by FTIR method: (a) (b) Surface and column water samples in rainy season; (c) (d) Surface and column water samples in dry season.\u003c/p\u003e","description":"","filename":"7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7419673/v1/8eadb9198e29854b615cfaf6.jpg"},{"id":93007636,"identity":"4479bf98-b517-4064-9ccc-e2e23dd27999","added_by":"auto","created_at":"2025-10-08 06:54:16","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":64605,"visible":true,"origin":"","legend":"\u003cp\u003ePollution load index (PLI) of the MPs in water samples in 08 locations and in two seasons: (a) for sampling locations; (b) (for sampling season.\u003c/p\u003e","description":"","filename":"8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7419673/v1/8457bd81f6e4bac08a851b7f.jpg"},{"id":93945496,"identity":"a715abb8-0791-414a-a545-8fee8f6672eb","added_by":"auto","created_at":"2025-10-20 14:17:14","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2480404,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7419673/v1/619838e7-9d8b-424f-a02a-00986007304d.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Microplastic pollution and ecological risk in estuaries and coastal areas: A case study at Han River estuary, Da Nang city, Vietnam","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003ePlastic has become extremely popular in everyday life and possesses some advantage features in comparison to other materials due to its versatility, affordability, durability, and resistance to a wide range of temperatures (Andrady \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Wootton et al. \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Its inert nature and long lifespan make it widely applicable in various industries, including household goods, personal items, textiles, packaging, and construction (Geyer et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Therefore, global plastic production has surged dramatically since its large-scale manufacturing began in the 1950s, reaching 413.8\u0026nbsp;million tons in 2023 (Plastics Europe 2023), causing increased potential risk to the ecosystem in general and human health in particular due to exposure. While a portion of plastic waste is managed through recycling or incineration (9%), vast quantities (90%) remain in the environment, contributing significantly to marine pollution (Geyer et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; OECD 2022). Over time, these plastics degrade into microplastics, which accumulate in water, sediments, and living organisms, posing severe threats to ecosystems, and human health. According to NOAA (2015) and FAO (\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), microplastics (MPs) are defined as tiny plastic pieces smaller than 5 mm in size and are emerging groups of pollutants that have received particular attention recently. They are diveded to two groups including primary and secondary MPs. Primary MPs are intentionally manufactured at small sizes for use in industrial products, personal care items, and abrasives, while secondary MPs are derived from the degradation of larger plastic debris due to environmental factors such as UV radiation, mechanical forces, and microbial activity (Lapyote et al. 2023). MPs are not only widely dispersed in freshwater and marine systems (Lin et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Xiong et al. \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Matias et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) but also accumulate in sediments and a variety of organisms, potentially posing risks to ecosystems and human health through seafood consumption (Horton et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eVietnam, like many other countries, is facing an escalating crisis of plastic pollution. As a rapidly developing nation with extensive coastlines and a high dependence on marine resources, Vietnam generates a substantial amount of plastic waste, much of which ends up in the environment. Among these, microplastics pose a unique challenge due to their persistence, ability to bioaccumulate, and potential toxic effects on aquatic organisms and human health. The water environment, particularly estuarine and coastal ecosystems, is highly susceptible to microplastic contamination. Estuaries, where freshwater meets seawater, serve as critical habitats for diverse marine species and act as natural filters for pollutants. However, they are also key accumulation zones for microplastics due to urban runoff, industrial discharge, and riverine inputs. The presence of microplastics in estuaries and coastal waters can lead to severe environmental consequences, including the disruption of aquatic food chains, habitat degradation, and threats to fisheries and public health.\u003c/p\u003e\u003cp\u003eThe Han River, located in Da Nang City, Vietnam, is a vital waterway that flows through the heart of the city before emptying into the East Sea. As a dynamic estuarine system, it is subject to various anthropogenic influences, including urbanization, tourism, and industrial activities. The river plays a crucial role in the socio-economic development of Da Nang, supporting fisheries, transportation, and recreational activities. However, like many other riverine systems in Vietnam, the Han River is increasingly threatened by plastic pollution, particularly microplastics. Despite its significance, limited research has been conducted to assess the extent of microplastic contamination in the Han River estuary and its potential environmental impacts. Given the growing concern over plastic pollution in Vietnam\u0026rsquo;s aquatic environments, this study aims to investigate the status of microplastic contamination in water environment the Han River estuary. The research will focus on identifying the discharging sources, and characteristics of microplastics in the surface water and column water in the estuary. The findings will provide valuable insights into the extent of microplastic pollution in the region and contribute to the development of effective management strategies to mitigate its impact.\u003c/p\u003e\u003cp\u003eThis research aims to:\u003c/p\u003e\u003cp\u003e\u003col\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eAssess the abundance and characteristics of microplastics in the Han River estuary.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eIdentify the potential sources of microplastic pollution in the study area.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eEvaluate the ecological risks associated with microplastic contamination in the estuarine environment.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003c/ol\u003e\u003c/p\u003e\u003cp\u003eUrgency of the Study\u003c/p\u003e\u003cp\u003eThe rapid increase in plastic pollution in Vietnam\u0026rsquo;s water environments, particularly in estuaries and coastal ar eas, calls for immediate attention. Microplastic contamination poses serious threats to biodiversity, water quality, and human health, necessitating urgent research and policy interventions. The Han River estuary, as a crucial water body in Da Nang City, requires systematic assessment to understand the severity of microplastic pollution and formulate appropriate mitigation strategies. This study is expected to fill critical knowledge gaps and contribute to sustainable water resource management in Vietnam. By addressing these key issues, the study will not only enhance scientific understanding of microplastic pollution in estuaries but also provide a foundation for future environmental conservation efforts in Da Nang and other coastal cities in Vietnam.\u003c/p\u003e"},{"header":"2. Methodology","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1. Characteristics of area study\u003c/h2\u003e\u003cp\u003eDa Nang, situated in the South-Central region of Vietnam, holds a pivotal position as the most significant urban center in the Central region. It serves as a hub for various sectors, including economics, finance, politics, culture, tourism, society, education, science, and technology. Geographically, Da Nang is located between latitudes 15\u0026deg;55' and 16\u0026deg;14' North, and longitudes 107\u0026deg;18' and 108\u0026deg;20' East. The Han River is one of the four principal rivers in Da Nang City along with the Vu Gia, Cu De, and Phu Loc rivers, plays a crucial role in supporting the city\u0026rsquo;s socio-economic development. It is located downstream of the Thu Bon River and originates at the confluence of the Cam Le and Vinh Dien rivers. The Han River extends approximately 7.2 kilometers and flows through the urban area. There are many restaurants, hotels and people living on both sides of the river. This is also a famous and important tourist destination of the city. Waterway traffic and fishing activities in the estuary also generate a lot of organic waste into the environment, including plastic. The eight sampling sites, positioned along a transect from Tien Son Bridge toward Da Nang Bay (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e and Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), were characterized by the presence of various sources of waste or human activities associated with waste discharge.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eSampling location characteristics\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"4\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNo.\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSampling Location\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eSample Code\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eDescription\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eTien Son Bridge\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eĐN1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eLocated near residential areas of My An, Hoa Cuong Bac, and Hoa Cuong Nam wards in Ngu Hanh Son District.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eTran Thi Ly Bridge\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eĐN2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eSurrounded by residential areas and restaurants, near Green Island villa area and Dinh Tien Hoang Primary School in Binh Thuan Ward.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eRong Bridge\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eĐN3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eAdjacent to residential areas and numerous restaurants in An Hai Tay and Hai Chau 1 Wards.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eHan River Bridge\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eĐN4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eFlanked by hotels, restaurants, and supermarkets in An Hai and Son Tra Wards, within Hai Chau and Son Tra Districts.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCity Discharge Drain\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eĐN5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eThis location marks the discharge point from Da Nang City into the Han River, near Da Phuoc (Old) fishing port and Da Nang Marina in Thuan Phuoc and Hai An Bac Wards.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eThuan Phuoc Bridge\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eĐN6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eSituated near the Thuan Phuoc lighthouse, surrounded by hotels and restaurants, with no residential areas, in Thuan Phuoc and Nai Hien Dong Wards.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eDa Nang Bay 7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eĐN7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eLocated at the confluence of the Han River and Da Nang Bay, approximately 700 meters from Thuan Phuoc Bridge (ĐN6).\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eDa Nang Bay 8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eĐN8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eSituated 800 meters from ĐN7 within Da Nang Bay, with no surrounding residential areas.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2. Sampling Method\u003c/h2\u003e\u003cp\u003eThe sampling method was conducted following established protocols outlined in previous studies (Masura et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Sliva et al. 2017). A neuston mesh net with a mesh size of 330 \u0026micro;m was either mounted on a water collection box or integrated with a Manta trawl net (dimensions: 30 x 30 x 15 cm, D x W x H). A flowmeter was affixed to the system to measure the volume of water filtered during sampling. At every location, the equipment was secured to boats, and the collection boxes were allowed to float on the water surface ranging from 30 to 60 minute to capture all solid particles present in both the surface layer and water column, including plastic debris and other suspended solids. The samples were conducted spanning from rainy season (October 2023) to dry season (May 2024). All collected samples were stored in dark glass containers at 4\u0026deg;C and transported to the laboratory on the same day for further analysis.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3. Analysis Methods\u003c/h2\u003e\u003cp\u003eThe identification and characterization of microplastics were conducted using the wet peroxide oxidation method. Firstly, 300 mL of original wastewater was wet sieved by a stainless-steel mesh screen 5 mm. The sieved samples containing particles smaller than 5 mm remained for next experiments. Subsequently, the samples were pretreated to remove organic matter by adding solution 30% hydrogen peroxide (H₂O₂) and the Fe(II) 0.05 M (Merck, Germany) at 40\u0026deg;C for 48 hours, following modified NOAA procedures (Masura et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Density separation was then conducted to isolate microplastics. A saturated NaI solution (density\u0026thinsp;\u0026asymp;\u0026thinsp;1.6 g/cm\u0026sup3;) was added to the digested samples. The mixture was allowed to settle, and the supernatant was collected and filtered through a 1.6 \u0026micro;m pore size glass fiber filter (Whatman, Germany) by vacuum pump and glass filtration apparatus (Duran, Germany). The microplastic characteristics such as quantity, size, shape and color were observed under optical stereomicroscope (MSZ5000-T-IL-TL, Kruss, Germany) (Masura et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eFor Fluorescence Microscope method, the microplastics was stained by Nile Red (9-diethylamino-5H-benzo[α]phenoxazine-5-one), a lipophilic dye that preferentially binds to hydrophobic plastic surfaces. The staining procedure followed methods adapted from Erni-Cassola et al. (\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Each sample filter was stained with 1 mL of Nile Red working solution (1\u0026micro;g/mL in ethanol) and incubated in the dark at room temperature for 30 minutes. After staining, filters were gently rinsed with deionized water and dried in a petri dish under a hood cabinet. Filters were examined under a fluorescence microscope and only particles fluorescing after Nile Red staining and confirmed via morphology were counted as microplastics. The microplastic characteristics such as quantity, size, and shape were observed with Fluorescence Microscope (AXIO Zoom V16, Zeiss, Germany).\u003c/p\u003e\u003cp\u003eThen, the quantity, size and polymer types present in the samples were also classified with a FTIR-6800 system (Nicolet iN10MX, USA). The spectra obtained from every sample were compared with the corresponding standard spectra in the spectral library (Jung et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Quality Assurance and Control: Strict anti-contamination protocols were implemented throughout sample processing. Procedural blanks were analyzed to ensure no interferences from lab materials. All substrates and tools used in analysis were cleaned with ethanol and deionized water and inspected before use.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e2.4 Pollution Load Index\u003c/h2\u003e\u003cp\u003eTo evaluate the MP pollution levels in the surface and column water of Han River, the integrated Pollutant Load Index (PLI) was applied in accordance with the method reported by Tomlinson et al. (\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e1980\u003c/span\u003e). The PLI index enables the classification of contamination risk such as below 10 categorized as (I) low risk, from 10 to 20 as (II) moderate risk, from 20 to 30 as (III) high risk, and above 30 as (IV) very high risk (Table S1). The PLI index was calculated using the following equation:\u003c/p\u003e\u003cp\u003ePLI\u003csub\u003eSi\u003c/sub\u003e = \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\sqrt{\\frac{{C}_{si}}{{C}_{0}}}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003cp\u003ePLI\u003csub\u003elocal\u003c/sub\u003e = \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\sqrt[n]{{{PLI}_{S1.}\\:{PLI}_{S2}\\dots\\:.PLI}_{Sn}}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003cp\u003eIn this formula, \u0026ldquo;Csi\u0026rdquo; refers to the MP concentration measured at each sampling location, whereas \u0026ldquo;C\u003csub\u003e0\u003c/sub\u003e\u0026rdquo; denotes the lowest MP abundance recorded in the present study, representing the uncontaminated condition due to the absence of an absolute zero reference value.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable S1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eClassification table of Pollution load index for MP pollution (Tomlinson et al., \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e1980\u003c/span\u003e; Ranjani et al., \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2021\u003c/span\u003e)\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"2\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePLI\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eRisk category\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u0026lt; 10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eLow risk\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e10\u0026ndash;20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eModerate risk\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e20\u0026ndash;30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eHigh risk\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u0026gt;30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eVery high risk\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003e2.5. Statistical data\u003c/h2\u003e\u003cp\u003eThe database in the present study is calculated by GraphPad 6 and Original 2019b software. The volume of water was recorded from the flowmeter for subsequent calculations. The density of microplastics was determined using the following formula (Do et al. 2022):\u003c/p\u003e\u003cp\u003e\u003cimg src=\"data:image/png;base64,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\" style=\"width: 51px; height: 28.5161px;\" width=\"51\" height=\"28.5161\"\u003e\u003c/p\u003e\u003cp\u003ewhere \u003cem\u003eC\u003c/em\u003e denotes the microplastic density (fragment, fiber, particle/m\u0026sup3;), \u003cem\u003en\u003c/em\u003e represents the number of microplastic items in the sample (fragment, fiber, particle), and \u003cem\u003eV\u003c/em\u003e corresponds to the volume of water filtered through the mesh (m\u0026sup3;).\u003c/p\u003e\u003c/div\u003e"},{"header":"3. RESULT AND DISCUSSION","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\u003ch2\u003e3.1. The microplastic density classification by quantity\u003c/h2\u003e\u003cp\u003eDifferent analytical methods showed different results and the results in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e2\u003c/span\u003e showed that the microplastic density in both two seasons are also very different. In the rainy season, the presence of microplastics was observed at all 8 sampling locations. The microplastic density was determined by stereomicroscope, Fluorescence Microscope and FTIR method varied from 1201, 1049, 1260 MPs.L\u003csup\u003e-1\u003c/sup\u003e in surface water samples to 1408, 1254, 1500 MPs.L\u003csup\u003e-1\u003c/sup\u003e in column water samples, respectively. The results also showed that ĐN6 consistently exhibited the highest microplastic density regardless of the analytical method applied. This finding is consistent with field observations, as the site is located near the municipal wastewater discharge area. The density of microplastics in the dry season is significantly different from the rainy season. These values decrease substantially and, in some locations (ĐN7 and ĐN1), microplastics even were not recorded at all. The corresponding density values were 148, 177 and 116 MPs.L\u003csup\u003e-1\u003c/sup\u003e in surface water samples and 123, 162 and 48 MPs.L\u003csup\u003e-1\u003c/sup\u003e in column water samples.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eTotal of microplastics in surface water (ĐN_SW) and water column (ĐN_CW) samples at Han River estuary were analyzed by three methods: stereomicroscope, Fluorescence Microscope and FTIR\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"7\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003eCode sample\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"6\" nameend=\"c7\" namest=\"c2\"\u003e\u003cp\u003eQuantity of microplastic in rainy season\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003eStereomicroscope method\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003eFluorescence Microscope method\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003eFTIR method\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eĐN_SW\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eĐN_CW\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eĐN_SW\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eĐN_CW\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eĐN_SW\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003eĐN_CW\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e50\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e171\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e45\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e150\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e50\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e180\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e220\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e194\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e195\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e168\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e225\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e205\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e49\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e142\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e35\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e110\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e50\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e150\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e49\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e187\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e41\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e178\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e55\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e200\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e108\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e137\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e95\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e115\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e120\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e145\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e489\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e334\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e416\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e320\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e500\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e360\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e92\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e148\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e90\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e128\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e105\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e155\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e144\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e95\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e132\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e85\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e155\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e105\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTotal\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1201\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1408\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e1049\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1254\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1260\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e1500\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003eCode sample\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"6\" nameend=\"c7\" namest=\"c2\"\u003e\u003cp\u003eQuantity of microplastic in dry season\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003eStereomicroscope method\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003eFluorescence Microscope method\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003eFTIR method\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eĐN_SW\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eĐN_CW\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eĐN_SW\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eĐN_CW\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003eĐN_SW\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003eĐN_CW\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e19\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e13\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e28\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e13\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e28\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e14\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e13\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e13\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e37\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e25\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e17\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e46\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e28\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e28\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e16\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e14\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e23\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e11\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e28\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e45\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e25\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e22\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e28\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e24\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e25\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTotal\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e148\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e123\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e177\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e162\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e116\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e48\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eThe findings of this study align with some previous research in estuaries area (Hidalgo-Ruz et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Liu et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Gao et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) but contrast with others (Lebreton et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Dai et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Tikhonova et al. \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). MPs abundance was consistently lower in the dry season than in the rainy season; in the rainy season, water column densities exceeded surface water, while the opposite was observed in the dry season. As noted by Hidalgo-Ruz et al. (\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2012\u003c/span\u003e) and Gao et al. (\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), low-density MPs can remain longer in surface layers, increasing organisms\u0026rsquo; exposure. The major source of MPs into the marine environment is through riverine systems, influenced by water depth, wind direction, flow velocity and human activities (Lebreton et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Dai et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Lenaker et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Tikhonova et al. \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e2\u003c/span\u003e showed that the number of microplastics detected varied markedly among the sampling locations, exhibiting a decreasing trend toward the river mouth. The last two locations recorded relatively low numbers of microplastics, a result consistent with their geographical characteristics, location, and surrounding landscape, as both riverbanks are uninhabited, and few services and production activities. Similar spatial patterns have been documented globally: Li et al. (\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) found higher MPs density in estuaries than offshore islands, while Diana et al. (\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) reported much higher concentrations in the Sado estuary (1042.8\u0026thinsp;\u0026plusmn;\u0026thinsp;430.8 MPs/kg) compared to coastal locations (52.9\u0026thinsp;\u0026plusmn;\u0026thinsp;31.9 MPs/kg), with densities increasing inland due to human activities. Further inland, microplastic density was found to increase, closely related to the daily activities of residents along both riverbanks.\u003c/p\u003e\u003cp\u003eMorever, MPs density is also affected by weather conditions and tidal regimes as well as regional rainfall and flooding. The coastal waters of Da Nang are influenced by a semi-diurnal tidal regime with an amplitude of about 0.6 m. The Han River, flowing uniquely from south to north into Da Nang Bay, is characterized by short length, steep slope, large flow fluctuations, and low sediment loads. During the rainy season, rapid floods occur but last only a few days, while in the dry season, reduced upstream supply lowers water levels and causes salinization. There are many residential areas, numerous restaurants, hotels, supermarkets, local markets located along its banks and a fishing port near the river mouth. A large amount of waste from terrestrial sources is received by the river during flood events, explaining the higher microplastic density in the rainy season. According to Lebreton et al. (\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2017\u003c/span\u003e), more than 74% of the annual plastic waste discharged from rivers occurs between May and October, as reported in the summary on microplastic pollution in Asia and East Asia. These results are consistent with regional studies and highlight surface runoff as the main mechanism transporting microplastics from land to river and into the marine environment (Andrady \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2017\u003c/span\u003e).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\u003ch2\u003e3.2. The microplastic density classification in size\u003c/h2\u003e\u003cp\u003eSize-based classification of microplastics showed seasonal differences across analytical methods. Using stereomicroscope and fluorescence microscope, smaller particles were dominant in the rainy season (20\u0026ndash;50, 50\u0026ndash;150, 100\u0026ndash;300, 300\u0026ndash;500, \u0026gt;\u0026thinsp;500 \u0026micro;m), while larger ones prevailed in the dry season (200\u0026ndash;500, 500\u0026ndash;1000, 1000\u0026ndash;1500, \u0026gt;\u0026thinsp;1500 \u0026micro;m). Although particles were sieved out, some long fibers (\u0026gt;\u0026thinsp;1.5 mm) were detected because their curled form allowed them to pass through the mesh before expanding during oxidation. In contrast, FTIR consistently identified five size categories: 20\u0026ndash;50, 50\u0026ndash;150, 100\u0026ndash;300, 300\u0026ndash;500, and \u0026gt;\u0026thinsp;500 \u0026micro;m.\u003c/p\u003e\u003cp\u003e\u003cb\u003ea) Stereomicroscope method\u003c/b\u003e\u003c/p\u003e\u003cp\u003eFor the classification using stereomicroscope, the rainy season survey showed that microplastics sized 300\u0026ndash;500 \u0026micro;m were most abundant in both surface water (631 MPs\u0026middot;L⁻\u0026sup1;) and water column (704 MPs\u0026middot;L⁻\u0026sup1;), while particles\u0026thinsp;\u0026gt;\u0026thinsp;500 \u0026micro;m were least common (37 and 60 MPs\u0026middot;L⁻\u0026sup1;, respectively). In surface water, the maximum count for 300\u0026ndash;500 \u0026micro;m particles was at location ĐN6 (265 MPs\u0026middot;L⁻\u0026sup1;) and the minimum for \u0026gt;\u0026thinsp;500 \u0026micro;m at ĐN4 location (2 MPs\u0026middot;L⁻\u0026sup1;); in the water column, the highest was also at ĐN6 location (116 MPs\u0026middot;L⁻\u0026sup1;) and the lowest at ĐN5 location (5 MPs\u0026middot;L⁻\u0026sup1;). During the dry season, microplastics of 200\u0026ndash;500 \u0026micro;m dominated, with 112 MPs\u0026middot;L⁻\u0026sup1; in surface water and 104 MPs\u0026middot;L⁻\u0026sup1; in the water column, followed by 500\u0026ndash;1000 \u0026micro;m (32 and 12 MPs\u0026middot;L⁻\u0026sup1;) and 1000\u0026ndash;1500 \u0026micro;m (3 and 6 MPs\u0026middot;L⁻\u0026sup1;). Microplastics\u0026thinsp;\u0026gt;\u0026thinsp;1500 \u0026micro;m were rare, detected only at ĐN1 location (surface water) and ĐN2 location (water column), and absent at other locations (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eThe microplastics size in surface water (ĐN_SW) and water column (ĐN_CW) samples at Han River estuary by stereomicroscope method\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"17\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c12\" colnum=\"12\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c13\" colnum=\"13\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c14\" colnum=\"14\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c15\" colnum=\"15\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c16\" colnum=\"16\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c17\" colnum=\"17\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003eCode sample\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"16\" nameend=\"c17\" namest=\"c2\"\u003e\u003cp\u003eSize of microplastic in the rainy season\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colspan=\"3\" nameend=\"c4\" namest=\"c2\"\u003e\u003cp\u003e20\u0026ndash;50 \u0026micro;m\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"3\" nameend=\"c7\" namest=\"c5\"\u003e\u003cp\u003e50\u0026ndash;150 \u0026micro;m\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"3\" nameend=\"c10\" namest=\"c8\"\u003e\u003cp\u003e150\u0026ndash;300 \u0026micro;m\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"4\" nameend=\"c14\" namest=\"c11\"\u003e\u003cp\u003e300\u0026ndash;500 \u0026micro;m\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"3\" nameend=\"c17\" namest=\"c15\"\u003e\u003cp\u003e\u0026gt;\u0026thinsp;500 \u0026micro;m\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eĐN_SW\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003eĐN_CW\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003eĐN_SW\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003eĐN_CW\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c8\"\u003e\u003cp\u003eĐN_SW\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e\u003cp\u003eĐN_CW\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e\u003cp\u003eĐN_SW\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c14\" namest=\"c13\"\u003e\u003cp\u003eĐN_CW\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c16\" namest=\"c15\"\u003e\u003cp\u003eĐN_SW\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c17\"\u003e\u003cp\u003eĐN_CW\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e21\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e33\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e\u003cp\u003e20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c14\" namest=\"c13\"\u003e\u003cp\u003e99\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c16\" namest=\"c15\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c17\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e45\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e38\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e33\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e\u003cp\u003e12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e\u003cp\u003e145\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c14\" namest=\"c13\"\u003e\u003cp\u003e104\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c16\" namest=\"c15\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c17\"\u003e\u003cp\u003e7\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e18\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e28\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e19\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e\u003cp\u003e9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e\u003cp\u003e12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c14\" namest=\"c13\"\u003e\u003cp\u003e81\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c16\" namest=\"c15\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c17\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e17\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e39\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e\u003cp\u003e11\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e\u003cp\u003e13\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c14\" namest=\"c13\"\u003e\u003cp\u003e98\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c16\" namest=\"c15\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c17\"\u003e\u003cp\u003e9\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e18\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e24\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e11\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e17\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e\u003cp\u003e11\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e\u003cp\u003e68\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c14\" namest=\"c13\"\u003e\u003cp\u003e79\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c16\" namest=\"c15\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c17\"\u003e\u003cp\u003e6\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e105\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e116\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e82\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e57\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e27\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e\u003cp\u003e39\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e\u003cp\u003e265\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c14\" namest=\"c13\"\u003e\u003cp\u003e110\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c16\" namest=\"c15\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c17\"\u003e\u003cp\u003e12\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e34\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e27\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e16\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e17\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e\u003cp\u003e27\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c14\" namest=\"c13\"\u003e\u003cp\u003e88\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c16\" namest=\"c15\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c17\"\u003e\u003cp\u003e6\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e29\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e22\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e21\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e\u003cp\u003e6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e\u003cp\u003e81\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c14\" namest=\"c13\"\u003e\u003cp\u003e45\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c16\" namest=\"c15\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c17\"\u003e\u003cp\u003e7\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTotal\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e274\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e306\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e172\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e230\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e87\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e\u003cp\u003e108\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e\u003cp\u003e631\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c14\" namest=\"c13\"\u003e\u003cp\u003e704\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c16\" namest=\"c15\"\u003e\u003cp\u003e37\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c17\"\u003e\u003cp\u003e60\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003eCode sample\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"16\" nameend=\"c17\" namest=\"c2\"\u003e\u003cp\u003eSize of microplastic in the dry season\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"4\" nameend=\"c5\" namest=\"c2\"\u003e\u003cp\u003e200\u0026ndash;500 \u0026micro;m\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"4\" nameend=\"c9\" namest=\"c6\"\u003e\u003cp\u003e500\u0026ndash;1000 \u0026micro;m\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"4\" nameend=\"c13\" namest=\"c10\"\u003e\u003cp\u003e1000\u0026ndash;1500 \u0026micro;m\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"4\" nameend=\"c17\" namest=\"c14\"\u003e\u003cp\u003e\u0026gt;\u0026thinsp;1500 \u0026micro;m\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003eĐN_SW\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003eĐN_CW\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003eĐN_SW\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003eĐN_CW\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c11\" namest=\"c10\"\u003e\u003cp\u003eĐN_SW\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c13\" namest=\"c12\"\u003e\u003cp\u003eĐN_CW\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c15\" namest=\"c14\"\u003e\u003cp\u003eĐN_SW\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c17\" namest=\"c16\"\u003e\u003cp\u003eĐN_CW\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003e14\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c11\" namest=\"c10\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c13\" namest=\"c12\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c15\" namest=\"c14\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c17\" namest=\"c16\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e17\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c11\" namest=\"c10\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c13\" namest=\"c12\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c15\" namest=\"c14\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c17\" namest=\"c16\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003e11\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c11\" namest=\"c10\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c13\" namest=\"c12\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c15\" namest=\"c14\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c17\" namest=\"c16\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003e17\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c11\" namest=\"c10\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c13\" namest=\"c12\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c15\" namest=\"c14\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c17\" namest=\"c16\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e11\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c11\" namest=\"c10\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c13\" namest=\"c12\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c15\" namest=\"c14\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c17\" namest=\"c16\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003e40\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e21\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c11\" namest=\"c10\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c13\" namest=\"c12\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c15\" namest=\"c14\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c17\" namest=\"c16\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003e12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c11\" namest=\"c10\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c13\" namest=\"c12\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c15\" namest=\"c14\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c17\" namest=\"c16\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e18\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c11\" namest=\"c10\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c13\" namest=\"c12\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c15\" namest=\"c14\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c17\" namest=\"c16\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTotal\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003e112\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e104\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e32\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003e12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c11\" namest=\"c10\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c13\" namest=\"c12\"\u003e\u003cp\u003e6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c15\" namest=\"c14\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c17\" namest=\"c16\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003eb) Fluorescence Microscope Method\u003c/b\u003e\u003c/p\u003e\u003cp\u003eSimilarly, fluorescence microscopy identified five size groups in the rainy season and four in the dry season. In the rainy season, microplastics were detected at all sites across all groups, with the highest concentration in the 300\u0026ndash;500 \u0026micro;m range (570 MPs\u0026middot;L⁻\u0026sup1; in surface water and 662 MPs\u0026middot;L⁻\u0026sup1; in the water column) and the lowest in the \u0026gt;\u0026thinsp;500 \u0026micro;m group (22 and 36 MPs\u0026middot;L⁻\u0026sup1;, respectively). In the dry season, the 200\u0026ndash;500 \u0026micro;m group dominated, reaching 148 MPs\u0026middot;L⁻\u0026sup1; in surface water and 140 MPs\u0026middot;L⁻\u0026sup1; in the water column. Microplastics\u0026thinsp;\u0026gt;\u0026thinsp;1500 \u0026micro;m were extremely rare, with only one particle (1 MPs\u0026middot;L⁻\u0026sup1;) detected in surface water and none in the water column (Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab5\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eThe microplastics size in surface water (ĐN_SW) and water column (ĐN_CW) samples at Han River estuary by Fluorescence Microscope method\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"17\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c12\" colnum=\"12\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c13\" colnum=\"13\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c14\" colnum=\"14\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c15\" colnum=\"15\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c16\" colnum=\"16\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c17\" colnum=\"17\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003eCode sample\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"16\" nameend=\"c17\" namest=\"c2\"\u003e\u003cp\u003eSize of microplastic in the rainy season\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colspan=\"3\" nameend=\"c4\" namest=\"c2\"\u003e\u003cp\u003e20\u0026ndash;50 \u0026micro;m\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"3\" nameend=\"c7\" namest=\"c5\"\u003e\u003cp\u003e50\u0026ndash;150 \u0026micro;m\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"3\" nameend=\"c10\" namest=\"c8\"\u003e\u003cp\u003e150\u0026ndash;300 \u0026micro;m\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"4\" nameend=\"c14\" namest=\"c11\"\u003e\u003cp\u003e300\u0026ndash;500 \u0026micro;m\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"3\" nameend=\"c17\" namest=\"c15\"\u003e\u003cp\u003e\u0026gt;\u0026thinsp;500 \u0026micro;m\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eĐN_SW\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003eĐN_CW\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003eĐN_SW\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003eĐN_CW\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c8\"\u003e\u003cp\u003eĐN_SW\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e\u003cp\u003eĐN_CW\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e\u003cp\u003eĐN_SW\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c14\" namest=\"c13\"\u003e\u003cp\u003eĐN_CW\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c16\" namest=\"c15\"\u003e\u003cp\u003eĐN_SW\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c17\"\u003e\u003cp\u003eĐN_CW\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e18\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e\u003cp\u003e11\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c14\" namest=\"c13\"\u003e\u003cp\u003e89\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c16\" namest=\"c15\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c17\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e36\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e32\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e27\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e28\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e\u003cp\u003e126\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c14\" namest=\"c13\"\u003e\u003cp\u003e95\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c16\" namest=\"c15\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c17\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e\u003cp\u003e7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c14\" namest=\"c13\"\u003e\u003cp\u003e73\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c16\" namest=\"c15\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c17\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e28\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e35\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e\u003cp\u003e9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e\u003cp\u003e11\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c14\" namest=\"c13\"\u003e\u003cp\u003e99\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c16\" namest=\"c15\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c17\"\u003e\u003cp\u003e7\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e14\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e18\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e\u003cp\u003e65\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c14\" namest=\"c13\"\u003e\u003cp\u003e72\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c16\" namest=\"c15\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c17\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e78\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e105\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e66\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e57\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e18\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e\u003cp\u003e36\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e\u003cp\u003e250\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c14\" namest=\"c13\"\u003e\u003cp\u003e114\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c16\" namest=\"c15\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c17\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e25\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e24\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e\u003cp\u003e25\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c14\" namest=\"c13\"\u003e\u003cp\u003e77\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c16\" namest=\"c15\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c17\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e25\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e16\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e\u003cp\u003e75\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c14\" namest=\"c13\"\u003e\u003cp\u003e43\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c16\" namest=\"c15\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c17\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTotal\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e212\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e266\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e180\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e201\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e65\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e\u003cp\u003e89\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e\u003cp\u003e570\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c14\" namest=\"c13\"\u003e\u003cp\u003e662\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c16\" namest=\"c15\"\u003e\u003cp\u003e22\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c17\"\u003e\u003cp\u003e36\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003eCode sample\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"16\" nameend=\"c17\" namest=\"c2\"\u003e\u003cp\u003eSize of microplastic in the dry season\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"4\" nameend=\"c5\" namest=\"c2\"\u003e\u003cp\u003e200\u0026ndash;500 \u0026micro;m\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"4\" nameend=\"c9\" namest=\"c6\"\u003e\u003cp\u003e500\u0026ndash;1000 \u0026micro;m\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"4\" nameend=\"c13\" namest=\"c10\"\u003e\u003cp\u003e1000\u0026ndash;1500 \u0026micro;m\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"4\" nameend=\"c17\" namest=\"c14\"\u003e\u003cp\u003e\u0026gt;\u0026thinsp;1500 \u0026micro;m\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003eĐN_SW\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003eĐN_CW\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003eĐN_SW\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003eĐN_CW\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c11\" namest=\"c10\"\u003e\u003cp\u003eĐN_SW\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c13\" namest=\"c12\"\u003e\u003cp\u003eĐN_CW\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c15\" namest=\"c14\"\u003e\u003cp\u003eĐN_SW\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c17\" namest=\"c16\"\u003e\u003cp\u003eĐN_CW\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003e21\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c11\" namest=\"c10\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c13\" namest=\"c12\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c15\" namest=\"c14\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c17\" namest=\"c16\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003e11\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c11\" namest=\"c10\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c13\" namest=\"c12\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c15\" namest=\"c14\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c17\" namest=\"c16\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e27\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003e9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c11\" namest=\"c10\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c13\" namest=\"c12\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c15\" namest=\"c14\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c17\" namest=\"c16\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003e41\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e27\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c11\" namest=\"c10\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c13\" namest=\"c12\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c15\" namest=\"c14\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c17\" namest=\"c16\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003e19\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c11\" namest=\"c10\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c13\" namest=\"c12\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c15\" namest=\"c14\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c17\" namest=\"c16\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003e19\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e27\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c11\" namest=\"c10\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c13\" namest=\"c12\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c15\" namest=\"c14\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c17\" namest=\"c16\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003e21\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c11\" namest=\"c10\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c13\" namest=\"c12\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c15\" namest=\"c14\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c17\" namest=\"c16\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003e6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e22\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c11\" namest=\"c10\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c13\" namest=\"c12\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c15\" namest=\"c14\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c17\" namest=\"c16\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTotal\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003e148\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e140\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e24\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003e20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c11\" namest=\"c10\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c13\" namest=\"c12\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c15\" namest=\"c14\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c17\" namest=\"c16\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003ec) FTIR method\u003c/b\u003e\u003c/p\u003e\u003cp\u003eIn contrast, FTIR classification identified only five size groups in both seasons. During the rainy season, the 50\u0026ndash;150 \u0026micro;m group showed the highest density (655 MPs\u0026middot;L⁻\u0026sup1; in surface water and 675 MPs\u0026middot;L⁻\u0026sup1; in the water column), while the 300\u0026ndash;500 \u0026micro;m group had the lowest values (80 and 90 MPs\u0026middot;L⁻\u0026sup1;, respectively). Microplastics from all five groups were found at most locations, except ĐN8 location (Table\u0026nbsp;\u003cspan refid=\"Tab6\" class=\"InternalRef\"\u003e5\u003c/span\u003e). In the dry season, overall densities declined, but the 50\u0026ndash;150 \u0026micro;m group remained dominant (48 MPs\u0026middot;L⁻\u0026sup1; in surface water and 16 MPs\u0026middot;L⁻\u0026sup1; in the water column). Other groups appeared sporadically, with many locations showing no detection. The \u0026gt;\u0026thinsp;500 \u0026micro;m group recorded the lowest values (12 and 4 MPs\u0026middot;L⁻\u0026sup1;, respectively), detected only at ĐN3, ĐN4, and ĐN6 locations (Table\u0026nbsp;\u003cspan refid=\"Tab6\" class=\"InternalRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab6\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eThe microplastics size in surface water (ĐN_SW) and water column (ĐN_CW) samples at Han River estuary by FTIR method\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"11\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003eCode sample\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"10\" nameend=\"c11\" namest=\"c2\"\u003e\u003cp\u003eSize of microplastic in the rainy season\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003e20\u0026ndash;50 \u0026micro;m\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e50\u0026ndash;150 \u0026micro;m\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e150\u0026ndash;300 \u0026micro;m\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003e300\u0026ndash;500 \u0026micro;m\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c11\" namest=\"c10\"\u003e\u003cp\u003e\u0026gt;\u0026thinsp;500 \u0026micro;m\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eĐN_SW\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eĐN_CW\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eĐN_SW\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eĐN_CW\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eĐN_SW\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003eĐN_CW\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c8\"\u003e\u003cp\u003eĐN_SW\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c9\"\u003e\u003cp\u003eĐN_CW\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c10\"\u003e\u003cp\u003eĐN_SW\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c11\"\u003e\u003cp\u003eĐN_CW\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e25\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e80\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e20\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e35\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e70\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e110\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e90\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e45\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e40\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e55\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e20\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e80\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e25\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e70\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e25\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e45\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e35\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e35\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e55\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e25\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e20\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e60\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e115\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e310\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e190\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e55\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e40\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e25\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e50\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e50\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e95\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e35\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e45\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e90\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e40\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e25\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTotal\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e240\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e430\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e655\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e675\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e155\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e180\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e80\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e90\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e130\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e125\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003eCode sample\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"10\" nameend=\"c11\" namest=\"c2\"\u003e\u003cp\u003eSize of microplastic in the dry season\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003e20\u0026ndash;50 \u0026micro;m\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e50\u0026ndash;150 \u0026micro;m\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e150\u0026ndash;300 \u0026micro;m\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003e300\u0026ndash;500 \u0026micro;m\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c11\" namest=\"c10\"\u003e\u003cp\u003e\u0026gt;\u0026thinsp;500 \u0026micro;m\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eĐN_SW\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eĐN_CW\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eĐN_SW\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eĐN_CW\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003eĐN_SW\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003eĐN_CW\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003eĐN_SW\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003eĐN_CW\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003eĐN_SW\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003eĐN_CW\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e24\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eĐN8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTotal\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e28\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e48\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e16\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e16\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eThe results also highlighted heterogeneity in microplastic sizes across surface and column water samples. Variations between analysis methods may explain the observed discrepancies, as the two types of microscopes yielded different distributions by size group, though the exact reason remains unclear. Nonetheless, most microplastics were concentrated in the \u0026lt;\u0026thinsp;500 \u0026micro;m size range (Tables\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e3\u003c/span\u003e, \u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e4\u003c/span\u003e, and \u003cspan refid=\"Tab6\" class=\"InternalRef\"\u003e5\u003c/span\u003e), and in some locations no microplastics of other size classes were detected. This suggests that microplastic pollution has persisted in the area surveyed over an extended period. Over time, smaller-sized microplastics become more easily transported by wind and water, leading to gradual accumulation in the environment. Similar patterns have been reported in previous studies (Mato et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2001\u003c/span\u003e; Teuten et al. \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Hernandez et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Alam et al. 2019). Plastic debris has also been shown to interact with biological processes and facilitate pollutant accumulation due to its strong adsorption capacity (Mato et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2001\u003c/span\u003e; Teuten et al., \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). Larger microplastics can degrade into smaller particles under the influence of sunlight, wind, and hydrodynamic forces when persisting in the environment for a long time. Lenaker et al. (\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) further demonstrated that polymer density decreases with depth in the water column and that microplastics tend to accumulate in sediments as they are transported from discharge points to estuarine areas.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003e3.3. The microplastic density classification in shape\u003c/h2\u003e\u003cp\u003eFour microplastic types were detected in both surface and water column samples at the Han River estuary including fibers, fragments, particles, and others. All three methods showed that fragments dominated in the rainy season and fibers in the dry season (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003ea) Stereomicroscope method\u003c/b\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eStereomicroscopy analysis showed that in the rainy season, fragments were dominant in both surface and water column samples, accounting for up to 60.13%, followed by fibers (36% and 33.33%). Particles and other types were less abundant, ranging from 0.58% in surface water to 5.87% in column water (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). In contrast, during the dry season, fibers were dominant (47% in surface water and 65.4% in column water), while fragments were secondary (26.8% and 18.5%). The remaining forms varied between 2.4% (column water) and 22.5% (surface water) (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003cb\u003eb) Fluorescence Microscope Method\u003c/b\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFluorescence microscopy showed a clear seasonal shift in microplastic forms. During the rainy season, fragments dominated, accounting for 62.92% of water column samples and 69.25% of surface water, followed by fibers (31.64% and 27.37%). Other forms were rare, ranging from 0.20% in surface water to 4.96% in the water column (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). In the dry season, fibers became predominant (69.93% in the water column and 54.15% in surface water), while fragments ranked second (23.44% and 39.42%). The proportions of other forms remained low, between 2.15\u0026ndash;4.28% in surface water and 3.18\u0026ndash;3.46% in the water column (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003cb\u003ec) FTIR method\u003c/b\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFTIR analysis identified only fragments and fibers in both surface and column water samples, in contrast to stereomicroscope and fluorescence methods, which detected additional forms (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). In the rainy season, fragments were dominant, accounting for 65.08% in surface water and 62.10% in the water column, followed by fibers (32.14% and 30.67%); particles were detected at low proportions (2.78% and 7.27%). No other shapes were observed. In the dry season, only fragments and fibers were recorded, with fibers prevailing in both surface and column water (58.62% and 58.33%), while fragments accounted for 41.38% and 41.67%, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThe distribution of microplastic forms in both surface and column water samples showed clear seasonal and vertical variations, influenced by hydrological conditions and water dynamics, making MPs form an important pollution indicator (Pushan et al. \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). In this study, fragments dominated during the rainy season, while fibers were predominant in the dry season. The rainy-season dominance of fragments likely resulted from surface runoff and hydrodynamic forces (e.g., heavy rainfall, turbulent flow) breaking down larger plastics, consistent with findings in Da Nang (Nguyen et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Do et al. 2022) and other regions in Vietnam (Nguyen et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Nguyen et al., \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Strady et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Fragments, often derived from packaging, cleaning products, cosmetics, and containers (Wu et al. \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), were abundant due to floods transporting large debris downstream for mechanical degradation. In contrast, low flow in the dry season allowed fibers - mainly from discarded fishing gear (Montarsolo et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) - to dominate, as reduced physical disruption favored their persistence. Other forms such as foam and particles occurred at lower levels but remain concerned about their potential toxicity to aquatic organisms (Tanaka and Takada \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2016\u003c/span\u003e).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003e3.4. The microplastic density classification in colors\u003c/h2\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFor color classification, only the stereomicroscope method was applied, as other techniques could be affected by equipment or staining interference. Results showed clear seasonal variations. In rainy season, white microplastics were dominant, accounting for 45% in surface water and 52.3% in column water, followed by blue (25.4% and 20.2%), green (15.9% and 15.9%), red (9.4% and 7.1%), and others (4.3% and 4.5%). In contrast, during the dry season, green microplastics were most abundant (49.5% in surface water and 46.7% in column water). White ranked second in surface water (22.9%), whereas black ranked second in column water (20.6%). The remaining colors showed lower proportions, with 13.9%, 5.8%, and 7.9% in surface water and 15.7%, 5.5%, and 11.5% in column water for white/black, red, and other colors, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThe color of microplastics has been considered of particular concern because they can be mistaken for food by aquatic organisms (Cole et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; S\u0026aacute; et al. \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Li et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Furthermore, color also indicates initial information regarding plastic production (Klein et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). In fact, colorless or transparent microplastics may be overlooked during extraction or identification. The results of this study are consistent with many previous publications showing that white is the dominant color among the recorded colors. Corcoran et al. (\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2015\u003c/span\u003e) noted that white microplastics were significantly more abundant than other colors, followed by pink and purple plastics. Li et al. (\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) also showed that white accounted for 64.7% of the total microplastics detected in sediments at the Yangtze River estuary (China), followed by blue, transparent, yellow, black, red, brown, and green. In this study, there was a difference in the dominant color between the two seasons. White and blue were dominant in the rainy season and white and green were dominant in the dry season. This may be because blue MP often originates from blue nylon lines of nets used in fishing activities, while white may originate from fishing gear (e.g., fishing lines and nets) (Jabeen et al. 2017) and may also fade due to weather (Hidalgo-Ruz et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). According to our field survey, most restaurants, hotels, residents, and traditional markets along both sides of the Han River primarily use white, green, or blue plastic bags, while fishing nets are typically white and green.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\u003ch2\u003e3.5. The microplastic density classification by polymer forms\u003c/h2\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003ePolymer types of microplastics in water samples were identified using FTIR method (Fourier-transform infrared spectroscopy). In rainy season, 22 polymer types with a total of 1.260 and 1500 MPs\u0026middot;L⁻\u0026sup1; were recorded in surface and column water samples such as PET (Polyethylene terephthalate), Nylon, Olefin, Polyester, Evoh Eval Film, Cellophane, Teflon, HDPE (High Density Polyethylene), LDPE (Low Density Polyethylene), PVC (Polyvinyl chloride)\u0026hellip;. PET and nylon polymers were the most dominant polymer types in surface and column water samples with values of 61.47; 11.47% and 62.29; 11.65%, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e). Other polymer types were observed inconsistently across locatons with the lower proportions. In contrast, results from the dry season showed a substantial reduction in both the number and concentration of identified polymer types. Only five and sixpolymer types were found in surface and column water samples with values of 116 and 48 MPs\u0026middot;L⁻\u0026sup1;, respectively. No polymers were detected at ĐN7 location. PET and Nylon also were predominant in surface and column water samples with values of 51.72; 34.48% and 16.67; 25%, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThe FTIR spectral analysis provided further confirmation of previously reported patterns of MPs pollution in estuarine and coastal waters. Consistent with the results obtained for MPs density, morphology, size, and color, the diversity of polymer types exhibited clear seasonal variation. In rainy season, 22 polymer types were identified, whereas only 6 polymer types were recorded in dry season. PET and PP are widely recognized as the most prevalent polymers in aquatic environments (Klein et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Li et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Diana et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). For example, Li et al. (\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) reported PET and PP proportions of 37.3 and 28.6% in Yangtze River estuary (China), while Diana et al. (\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) found PET to account for 41% in the Sado River estuary (Portugal). Similarly, Klein et al. (\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2015\u003c/span\u003e) detected up to 75% PET, PP, and polystyrene (PS) in the Rhine and Main rivers (Germany). In the present study, PET consistently dominated across seasons and sample types with 61.47% and 62.29% of MPs in surface and column water samples in rainy season, and this proportion in the dry season was 51.72% and 16.67%, respectively. Interestingly, nylon was the second most abundant polymer, comprising 11.47\u0026ndash;11.65% in rainy season and rising sharply to 25-34.48% in dry season. This finding reflects the widespread use of nylon bags in commercial and domestic activities along both sides of the Han River. Minor polymers such as olefins, Teflon, and phenol resins were also detected, indicating diverse plastic inputs. For instance, olefins were likely introduced from fuel leakage associated with tourist boats, fishing ports, and naval vessels near the river mouth. Overall, the dominant polymers detected (PET, PE, PP, PS) correspond to widely produced plastics characterized by low cost, high consumption volume, and broad applications in both industry and daily life. Polyethylene (PE) is commonly used for bags, bottles, and packaging (Wu et al. \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Wang et al. \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), PET originates largely from textiles (Gedik and Eryaşar \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2020\u003c/span\u003e), PP is applied in agricultural films and packaging, and PS is employed in food containers, jewelry, and fishing gear (Klein et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Zhou et al. 2016).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\u003ch2\u003e3.6. Risk Assessment\u003c/h2\u003e\u003cp\u003eCurrently, the ecological risk index has been used to assess the risk of microplastics (MPs) in various ecosystems such as coastal sediments, estuaries, soils, mangrove forests, and the atmosphere (Tomlinson et el. 1980; Barletta et al. 2016; Deng et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Pegado et al. \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Nishitha et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Therefore, the Pollution Load Index (PLI) value was applied in this study to evaluate the ecological risk at the Han River estuary area, Da Nang, Vietnam (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e). The results indicated that all surveyed locations have low levels of MP pollution, with PLI values ranging from 0.89 (ĐN6 in surface water and ĐN2, ĐN8 in column water in dry season) to 9.59 (ĐN6 surface water in rainy season) (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ea). The PLI\u003csub\u003elocal\u003c/sub\u003e analysis revealed that the study area exhibited a low pollution load, with an average PLI value of 1.74 (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003eb), categorized as \"Hazard Level I\" (\u0026lt;\u0026thinsp;10 on the risk classification scale - Table S1). Although microplastic pollution was classified as low, it can still pose serious threats to ecosystem health, causing nutrient loss, gastrointestinal blockage in organisms, and the release of toxic substances. Moreover, MPs may act as vectors for other contaminants such as persistent organic pollutants and heavy metals, amplifying ecological risks and potentially impacting human health through the food chain.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe Han River in Da Nang, Vietnam, is a key waterway supporting fisheries, transport, and recreation, but urban activities such as restaurants, markets, hotels, fishing, and ship repair yards are microplastic discharge potential sources. Monitoring these sectors is essential to reduce emissions and prevent higher PLI values that may harm ecosystems and communities in the future. Results show clear seasonal patterns: fragments dominate during high-flow conditions, while fibers prevail under low-flow conditions, especially in surface water. Vertical variation highlights differences in transport and sinking behavior, underscoring the need for stratified and seasonal monitoring of microplastics in aquatic systems.\u003c/p\u003e\u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eThis study analyzed microplastic characteristics in surface and column water from the Han River estuary (Vietnam) across rainy and dry seasons, focusing on abundance, morphology, color, polymer composition, and risk assessment. Microplastics were found at all locations, with higher densities in the rainy season, and in column water during the rainy but not the dry season. Microfragments and microfibers of smaller size dominated, with white as the most common color, followed by blue, green, and red. Spatial variation reflected human activities along both riverbanks. These findings provide baseline data for the South-Central Coast estuaries and support further studies on toxicity, transport, and ecological impacts. Although the Pollution Load Index indicated \u0026ldquo;Hazard Level I,\u0026rdquo; suggesting low risk, potential ecological impacts remain a concern. Thus, detailed classification of plastic types and stronger policies to regulate plastic use are needed to mitigate microplastic pollution.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003ch2\u003eConflicts of interest\u003c/h2\u003e\u003cp\u003eThe authors confirm that there are no conflicts of interest associated with this publication.\u003c/p\u003e\u003c/p\u003e\u003ch2\u003eFunding statement\u003c/h2\u003e\u003cp\u003eThis article was developed as part of project KC562, code ĐTĐL.CN\u0026thinsp;\u0026divide;\u0026thinsp;53/22, titled 'Research and assessment of the accumulation and impact of microplastics on the estuarine ecosystem along the South-Central Coast'. The authors gratefully acknowledge the Vietnam Ministry of Science and Technology for funding the project and supporting the completion of this article.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eWriting-original draft and Writing-review \u0026amp; editing: Tran Thi Thu Huong; Database analysis and software: Tran Thi Thu Huong, Vu Thu Van, Hoang Van Luong; Investigation, collection samples and Analysis methodology: Nguyen Thi Thanh Hoai, Ta Le Dang Khoi, Le Trung Son, Nguyen Lai Thanh, Nguyen Van Hanh, Tran Anh Quan, Pham Xuan Nui, Vu Kim Thu, Bui Thi Thu, Le Hung Phu, Vu Thu Van, Nguyen Bich Ngoc, Hoang Van Luong, Tran Thi Thu Huong. All authors have read and agreed to the published version of the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThis article was developed as part of project KC562, code ĐTĐL.CN\u0026divide;53/22, titled 'Research and assessment of the accumulation and impact of microplastics on the estuarine ecosystem along the South-Central Coast'. The authors gratefully acknowledge the Vietnam Ministry of Science and Technology for funding the project and supporting the completion of this article.\u003c/p\u003e\u003ch2\u003eData availability\u003c/h2\u003e\u003cp\u003eAll supplementary data and figures related to this study are provided within the article and are readily accessible.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAndrady, A. L. (2017). 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Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences, Yantai.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Microplastics, water column, surface water, pollution, Pollution Load Index (PLI)","lastPublishedDoi":"10.21203/rs.3.rs-7419673/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7419673/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eMicroplastics (MPs) pollution has been identified as a significant environmental concern in various ecosystems, including estuarine and coastal waters. In this study, surface and column water samples from the Han River (Vietnam) were collected during the rainy season of 2023 and the dry season of 2024 and analyzed. Microplastic characteristics were determined based on quantity, shape, size, color, polymer composition, and Pollution Load Index (PLI). Microplastics were detected at all sampling locations, with marked spatial and seasonal variability. Total MPs abundance in the dry season was consistently lower than in the rainy season. In the rainy season, MPs density in column water exceeded that in surface water, whereas the reverse pattern was observed in the dry season. Microfragments and microfibers of smaller size classes predominated. White was the most common color, followed by blue, green, red, and other colors. The number of polymer types in the rainy season was 22 and decreased to 5–6 in the dry season. Polyethylene terephthalate (PET) accounted for the highest proportion of all samples. The calculated PLI value (1.74) was classified as “Hazard Level I,” indicating a low pollution load; however, the potential environmental risks posed by microplastics remain a concern.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eClinical trial number: not applicable\u003c/strong\u003e\u003c/p\u003e","manuscriptTitle":"Microplastic pollution and ecological risk in estuaries and coastal areas: A case study at Han River estuary, Da Nang city, Vietnam","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-10-08 06:46:11","doi":"10.21203/rs.3.rs-7419673/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"310e0294-dc92-4a3d-8cc5-5256abb9c7e2","owner":[],"postedDate":"October 8th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-10-20T14:09:04+00:00","versionOfRecord":[],"versionCreatedAt":"2025-10-08 06:46:11","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7419673","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7419673","identity":"rs-7419673","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}